chore: update gatewayv1beta1 to gatewayv1 in examples and docs

[randmonkey]

What this PR does / why we need it:

update Gateways, GatewayClasses and HTTPRoutes in manifests of examples to gateway.networking.k8s.io/v1 and also their appearance in docs.

Which issue this PR fixes:

fixes #4891

Special notes for your reviewer:

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[team-k8s-bot]

Integration (targeted) tests with KIND-based cluster and latest images were started at https://github.com/Kong/kubernetes-ingress-controller/actions/runs/6608465283

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d8bbfd9) 77.7% compared to head (57ade56) 77.7%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4935     +/-   ##
=======================================
- Coverage   77.7%   77.7%   -0.1%     
=======================================
  Files        165     165             
  Lines      18477   18477             
=======================================
- Hits       14373   14367      -6     
- Misses      3281    3288      +7     
+ Partials     823     822      -1     

Files	Coverage Δ
...ternal/controllers/gateway/httproute_controller.go	76.7% <ø> (-1.1%)	⬇️
...rnal/dataplane/parser/translators/httproute_atc.go	92.9% <ø> (ø)

... and 7 files with indirect coverage changes

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[team-k8s-bot]

E2E (targeted) tests with KIND-based clusters were started at https://github.com/Kong/kubernetes-ingress-controller/actions/runs/6609261366